I would recommend contacting support to address the issue with getting your SMP server back up and running. As setting up a new SMP server could be more work then you want to deal with depending on what solutions you've got installed.

As far as ServiceDesk is concerned pointing it to a new SMP server is simply a matter of updating the SMP information in Credentials Manager. Once you've done this & restarted services it will start communicating with the new SMP.